Processes for preparing and utilizing partially de-ashed solid-fuel-water slurries and conveying the slurry by various conveying means, such as pumps, are known. O. Schwartz and H. Merten, Brennstoff Waerme Kraft 18 (10), 474-8 (1966) (Ger) describe a pilot plant in which coal was pulverized dry or wet in ball mills and disk grinders to provide particles up to 77% finer than 0.06 mm (60 .mu.m).
Other processes are described in U.K. Patent No. 711,105; French Patent No. 1,581,112; and U.S. Pats. Nos. 3,423,313; 3,682,114; 3,941,552; 3,950,147; and 3,996,026, all of which are discussed in applicant's copending U.S. Patent Aplication Ser. No. 790,337, filed Apr. 25, 1977, which portion of said application Ser. No. 790,337 is hereby incorporated by reference herein.
In addition to the above-listed patents, McMurtrie, U.S. Pat. No. 3,019,059, issued Jan. 30, 1962, describes a process for transporting finely divided coal solids by forcing through a conduit an aqueous slurry containing up to 50% solids and containing a minor proportion of coal acids which are added to improve pumpability and to prevent settling during pumping. At the receiving end of the conduit, the slurry is filtered or otherwise processed to remove the water and coal acids and to recover the coal solids for use. Alkali metal and ammonium salts of humic acids are included in the term "coal acids".
Also, Reichl, U.S. Pat. No. 3,073,652, issued Jan. 15, 1963 describes a method of transporting coal over long distances for conversion at distant locations which comprises obtaining coal having a spectrum of sizes and between about 20 and 40 percent by weight of (-)325 mesh particles, (-44 .mu.m), preparing a water slurry comprising between 35 and 60 percent by weight of said coal in water, pumping said slurry through a pipeline at a velocity of between about 3 and 7 feet per second over long distances to a distant location, interrupting the transportation of said slurry at said distant location, thereafter removing a portion of said water from said slurry to provide a concentrated slurry having a solids concentration of between 60 and 75 percent by weight of said coal in said water, pumping said concentrated slurry through a second pipeline over a shorter distance to a second location, and converting the coal in said concentrated slurry at said second location, or burning the concentrated slurry directly, if the burner is suitable for such burning.
Also, Clancey et al., U.S. Pat. No. 3,762,887, issued Oct. 2, 1973, describes a homogeneous composition of matter suitable for use as a liquid fuel consisting essentially of particulate coal and water in the relative proportions of 54 to 69 percent by volume of coal (61.3 to 75.0 wgt %) and 46 to 31 percent by volume of water, said particulate coal having a size distribution substantially as follows: 0 percent by weight on 4 mesh Tyler Standard screen, 18 to 33 percent by weight less than 325 mesh, less than 60 percent by weight between 4 and 28 mesh, and the balance in the size range of 28 to 325 mesh. The coal-water slurry is described as being pumpable, storable and directly burnable in a cyclone burner.
Commercially operated coal-slurry pipelines have been in operation for many years in the United States. Such pipelins and their successes, failures, and problems have been described in various publications, including the following:
"The Black Mesa Story" by F. H. Love, Pipeline Engineer, November 1969; PA0 "Slurry Pipelines, Energy Movers of the Future" by E. J. Wasp, and T. L. Thompson, Oil and Gas Journal, Dec. 24, 1973; PA0 "Research and Development for Slurry Pipeline System Design" by T. C. Aude and R. L. Gandhi, Bechtel, Inc., San Francisco, prepared for delivery at "The Second International Technical Conference on Slurry Transportation", Las Vegas, Nevada, Mar. 2-4, 1977; PA0 "Operating Experiences at the 1580 MW Coal Slurry Fired Mohave Generating Station" by M. L. Dina, presented at The International Conference on Slurry Transportation at Battelle Memorial Institute, Columbus, Ohio, Feb. 3, 1976; PA0 "Utilization of Pipeline Delivered Coal", by P. E. Snoek et al., Bechtel, Inc., San Francisco, for ASME Joint Power Generation Conference, Buffalo, N. Y., Sept. 20, 1976; and PA0 "Coal Slurry Pipelines", Van Nostrand Scientific Encyclopedia, fifth edition, 1976, page 58. PA0 (i) a coal compact comprising finely-divided coal particles having particle sizes in the range of about 1180 .mu.m to 0.05 .mu.m with at least 5 wgt. % of the particles being of colloidal size, said particles in said compact having a particle size distribution substantially in accordance with the following formula: ##EQU1## (ii) carrier water in an amount at least sufficient to transport said coal compact in a pipeline, PA0 (iii) counterion charged bound water layers on at least said particles of colloidal size, and PA0 (iv) an effective amount of at least one electrolyte and/or dispersing agent(s) present in said carrier water and providing counterions to said bound water layers on said particles in an amount sufficient to maintain the zeta potential at near maximum zeta potential and sufficient to disperse said coal particles. PA0 (i) providing a coal compact comprising finely-divided coal particles having particle sizes in the range of about 1180 .mu.m to 0.05 .mu.m with at least 5 wgt. % of the particles being of colloidal size, said particles in said compact having a particle size distribution substantially in accordance with the following formula: ##EQU2## (ii) providing carrier water in a total amount at least sufficient to transport said coal compact in a pipeline, PA0 (iii) determing the voltage and polarity of the zeta potential of a sample of coal particles from said coal compact when dispersed in a sample of said carrier water, PA0 (iv) determing from the results of step (iii) the type and amount of zeta potential enhancing electrolyte and/or dispersing agent(s) needed to adjust the zeta potential of at least the colloidal particles of said coal compact when mixed with said carrier water to a voltage near maximum zeta potential and sufficient to disperse said coal particles, PA0 (v) providing in said coal compact of step (i), or in said carrier water of step (ii), or in a mixture thereof the type and amount of zeta potential enhancing electrolyte and/or dispersing agent(s) determined to be needed from step (iv), PA0 (vi) blending said coal compact, carrier water, and electrolyte and/or dispersing agent(s) together to form said coal-water slurry. PA0 (i) pulverizing, in the presence of a pre-determined portion of the total amount of at least one electrolyte and/or dispersing agent(s) and in a minor amount of all the carrier water needed to transport said coal-water slurry in a pipeline, a first fraction of coal to prepare a pulverized dispersed coal fraction having particles substantially all finer than about 300 .mu.m, PA0 (ii) providing with a major amount of all said water and in the presence of the remaining portion said predetermined amount of said at least one electrolyte and/or dispersing agent(s) a second fraction of pulverized dispersed coal having coal particles of a fineness such that, when blended with said first fraction of coal particles to form a coal compact, the total blended mass will form a compact which contains a net of about 10 wgt. % of particles which are less than 3 .mu.m in size, PA0 (iii) blending said first and second fractions together in amounts by weight sufficient to provide a coal-water slurry having a coal compact with coal particles having a size in the range of about 300 .mu.m.times.0.1 .mu.m with at least about 10 wgt. % of said particles less than 3 .mu.m in size and distributed substantially in accordance with the following formula: ##EQU3## PA0 (iv) determining the voltage and polarity of the zeta potential of a sample of coal particles milled to &lt;10 .mu.m from said coal and dispersed in a sample of said carrier water, and PA0 (v) determing from the results of step (iv) the type and amount of zeta potential enhancing electrolyte and/or dispersing agent(s) needed to adjust the zeta potential of at least the colloidal particles of said coal compact when mixed with said carrier water to a voltage near maximum zeta potential and sufficient to disperse said coal particles. PA0 1. U.S. Series sieves Nos. 16, 20, 30, 40, 50, 70, 100, 140, and 200 were used to determine weights of coal particles passing through each sieve in the range of about (-) 1180 .mu.m to (-) 75 .mu.m, including D.sub.L where it is at least 75 .mu.m in size in the coal and the coal-water slurry. The cumulative weight percents of coal articles, dry basis, finer than (CPFT) a particular stated sieve size in microns were charted against the sizes in microns on a log-log chart, referred to herein as a "CPFT chart", to indicate the nature of the particle size distribution of 20 mesh .times. 200 mesh particles, substantially as shown in FIGS. 9-12. PA0 2. A Sedigraph 5500L (made by Micromeritics, Co., Ga., U.S.) was used to measure particle sizes and numbers of particles in coal and in the coal-water slurry in the range of (-) 75 .mu.m to about 0.3 .mu.m. The Sedigraph 5500L uses photo-extinction of settling particles dispersed in water according to Stoke's law as a means for making the above determinations. Although some measure of inaccuracy exists in measuring the range above 30 .mu.m and below 1 .mu.m, the determinations are found to be reasonably accurate and suitable for purposes of the invention in the range of 30 .mu.m to 0.1 .mu.m. Other instruments, such as a Coulter Counter can also be used for similar accuracy. The results were plotted on the above CPFT chart. PA0 3. A scanning electron microscope (SEM) at 40,000 .times. magnification was used to determine D.sub.S in the colloidal range below 1.0 .mu.m in the coal compact or in the coal-water slurry. The determination is made by preparing a dilute suspension of coal particles or by diluting a sample of disperse coal-water slurry to a dilution of about 10 wgt. % of coal per weight of solution. The dilute suspension is allowed to settle for two hours, (for example in a 100 ml graduate) and samples of the finest sizes are taken from the top one ml. of the suspension. This sample is further diluted with alcohol, and the diluted suspension or dispersion is examined on a copper pedestal using the SEM in a known way to find and measure the diameter, D.sub.S, of the smallest coal particle. This data is also plotted on the above CPFT chart. The plots from the three measurements are connected to obtain a "CPFT chart line", or curve.
The problem of preparing coal-water slurry for long distance delivery through pipelines ranging in diameter from about 4"to 48" to be burned at the delivery depot is to be distinguished from the problem of preparing a coal-water slurry from which a more concentrated slurry or a coal "cake" is prepared at a use site and burning the concentrated coal-water slurry or "cake" so prepared. Also, the problem of burning coal-water slurry in a turbulent burner is to be distinguished from burning coal-water slurry in a cyclone burner of a furnace. For examples of burners, see Chemical Technology: An Encyclopedic Treatment, J. F. Van Oss, Barnes and Noble Books, Div. Harper & Row, Publ., Inc. N.Y. 1971 Vol. II, Pages 722-725.